Heretofore, the prior art has suggested various forms of dashpot means for slowing the movement of a related means at some preselected point in its travel. It has been accepted practice to employ dashpot means in combination with or in association with engine carburetors, and other fuel metering devices, wherein, for example, it was desired to somewhat retard the otherwise relatively fast movement of the associated throttle means toward the curb idle position. The sole purpose of such prior art dashpot devices was to assure that the throttle would not close too rapidly as to thereby cause engine stalling. Accordingly, the operating specifications of such prior art devices were broadly stated and usually included broad tolerances since the problem of slowing the throttle valve velocity was not one requiring close tolerances or operating specifications.
It is still highly desirable to damp the rate of throttle closing movement near the end of such closing movement in order to avoid a very sudden change in the rate of air and fuel flow which, if permitted to occur, usually results in rough engine operation and/or engine stalling. However, because of governmentally imposed standards relating to engine fuel consumption and/or exhaust emissions, it has become important to be able to very critically control the rate of throttle closing movement. For example, in a piston type internal combustion engine, it is desirable to have the throttle return towards its closed (curb idle) position as quickly as possible in order to thereby reduce the rate of fuel flow to the engine (as occassioned by, for example, high air flows past the main fuel metering system) and yet, very closely to the end of such closing movement, retard such closing movement in order to avoid the creation of unburned hydrocarbons which would otherwise be emitted into the atmosphere through the engine exhaust.
The prior art structures have been found wanting in that the inherent designs thereof require manufacturing techniques which, in turn, result in assemblies which do not consistently have the degree of control required in order to be able to retard the closing movement of a throttle valve with the degree of exactness presently required.
By way of example, some of such prior art dashpot devices employed a bleed orifice which was comprised of a groove formed in a first surface (as possibly carried by the actuator or dashpot stem internally of the related housing) and a second surface (as possibly carried by a related diaphragm within the housing) which would lie against the first surface and thereby cooperate with the groove to define a bleed passage therethrough. Other prior art devices employed flapper-type valve portions which would cooperate with related orifices to control the bleed action therethrough. Still other prior art devices employed drilled restrictions as bleed orifice means. However, when it is realized that the actual volume rate of air flow through the bleed orifice means is very little, any slight dimensional variation from the theoretically ideal dimension in such elements comprising the prior art bleed orifice means will result in relatively great variations in the volume rate of air flow through that bleed orifice means.
Accordingly, the invention as herein disclosed and claimed is primarily directed toward the solution of the preceding as well as other related and attendant problems.